Edge improvement for window with electrically conductive layer

ABSTRACT

An electrically heatable window has a pair of outboard glass plys sandwiching a pair of transparent plastic interlayers which in turn sandwich a plastic ply or carrier film on which has been deposited an electrically conductive metal coating. Conductive bus bars contact edge portions of the conductive layer for applying a heating current. The conductive layer is applied to a large sheet of the carrier film which is subsequently cut to be co-extensive with the glass plys. The edge portions of the cut plastic ply have the conductive layer removed, preferably by abrasion, so that the edges of the plastic carrier film ply are bonded to the adjacent interlayer. This minimizes electrical hazards and protects the conductive layer from environmental attack.

United States Pate Levin Dec. 25, 1973 [75] Inventor: Berton P. Levin, Santa Monica,

Calif.

[73] Assignee: The Sierracin Corporation, Sylmar,

Calif.

[22] Filed: July 3, 1972 [21] Appl. No.: 268,827

2,982,934 5/1961 Browne 338/309 X 3,524,920 8/1970 Stromguist et a1... 219/543 X 3,659,079 4/1972 Whittemore 219/522 Primary Examiner-Velodymyr Y. Mayewsky AttorneyRobert L. Parker et a1.

[5 7] ABSTRACT An electrically heatable window has a pair of outboard glass plys sandwiching a pair of transparent plastic interlayers which in turn sandwich a plastic ply or carrier film on which has been deposited an electrically conductive metal coating. Conductive bus bars contact edge portions of the conductive layer for applying a heating current. The conductive layer is applied to a large sheet of the carrier film which is subsequently cut to be coextensive with the glass plys. The edge portions of the cut plastic ply have the conductive layer removed, preferably by abrasion, so that the edges of the plastic carrier film ply are bonded to the adjacent interlayer. This minimizes electrical hazards and protects the conductive layer from environmental attack.

2 Claims, 2 Drawing Figures BACKGROUND Electrically heatable Windshields and similar glazing has been used for many years in the aircraft industry so that pilots vision is not obscured by fog or ice formation. Such windows are made with glass and/or heavy transparent plastic layers on which conductive coatings are deposited. Typically such coatings are sandwiched into the final window rather than being on an external surface where they may be subject to mechanical damage. A Variety of metals, tin oxide and the like have been used for such conductive coatings. Typically aircraft Windshields and the like are made in relatively small numbers and a variety of sizes and shapes. For this reason it has been practical to make such windows on a one-at-a-time basis and the electrically conductive coatings are applied by batch type processing. The conductive coating is deposited only on areas where heating is desired and edges may be masked to prevent deposition in that portion.

It has become desirable to provide electrically heatable Windshields, back windows and the like for automobiles, trucks, snowplows, trains and the like; vhowever, with batch type application. of conductive coatings the cost may be prohibitive. Other approaches have been used, such as wires or frits embedded in the windows, however, these have not been completely satisfactory.

Recent developments have permitted the application of electrically conductive layers to plastic substrates on a continuous basis with sufficient control that the electrical properties of the conductive layer are suitable for fabrication of electrically heatable windows. Such continuous processing brings the cost down to commercially feasible numbers. Typically large sheets of thin transparent plastic carrier film are coated throughout one sidewith an electrically conductive coating. For example, various metals may be evaporated in a vacuum chamber and deposited on the carrier film with excellent adhesion and uniformity of the electrical properties. Thereafter, the carrier film is cut to a size and shape co-extensive with the other layers used'for laminating a windshield or the like,- and this assembly is bonded together by conventional techniques.

Some problem has been noted with electrically heatable Windshields made in this manner. The electrically conductive layers have a substantial resistance and, to obtain a sufficient watt density over the entire area of the window, voltages in the order 75 to l'volts may be involved. This and the substantial current in large size windows can present a safety hazard for persons touching the edges of the window while powered. Metal contact to the edge of the window may lead to anelectrical short. I

Further it has been found that environmental attack may occur in some instances at the interface where the conductive layer is present. Moisture and other contaminants may enter at this location and initiate delamination of the window. Addition of edge coatings to mechanically and chemically isolate the edges of the window has not proved entirely satisfactory. It is therefore desirable to provide a technique for minimizing electrical hazards and also providing environmental protection at the edges of a window having an electrically conductive layer between its faces.

BRIEF SUMMARY OF THE INVENTION Therefore in practice of this invention according to a presently preferred embodiment there is provided a window having a glass ply, a transparent plastic carrier film, a transparent conductive coating on one face of the carrier film, and a transparent plastic interlayer bonding the glass ply to the face of the carrier film having the conductive coating thereon. The conductive coating is removed from the edges of the carrier film before bonding the interlayer thereto.

DRAWINGS These and other features and advantages of the present invention will be appreciated as the same becomes better understood by reference to the following detailed description of a presently preferred embodiment when considered in connection with the accompanying drawings wherein:

FIG. 1 is a front view of a typical electrically heatable window constructed according to principles of this invention; and

FIG. 2 is a fragmentary cross section of an edge portion of the window of FIG. 1.

DESCRIPTION FIG 1 illustrates in front view a typical curved windshield for an automobile constructed according to principles of this invention. The windshield comprises a laminated glass panel 10 of the generally familiar character with means for electrically heating the windshield embedded in the plastic interlayer between two face sheets of glass. An electrically conductive bus bar 11 is provided along the bottom edge of the windshield and has a terminal 12 extending beyond the edge of the windshield for making electrical contact. Similarly there is a bus bar 13 along the upper edge of the windshield. A connecting bus bar 14 extends along one side edge of the windshield to a second terminal 16.

The center area 17 of the windshield is provided with a transparent electrically conductive layer between the sheets of glass. A narrow cut or scribe 18 is provided near the side edge of the windshield through the electrically conductive layer to provide electrical isolation of the central region 17 from the side portion 14 of the bus bar. Another. electrical isolation line is formed along the other side edge, although this is not necessary in all cases. The central region is, therefore, the only region electrically heated when current is passed between the bus bars 11 and 13. The scribe lines 18 are extremely shallow, barely going through the thin conductive layer and not going through the plastic carrier film substrate (hereinafter described) on which the layer is deposited.

FIG. 2 is a fragmentary cross section of the edge portion of the windshield showing several layers involved in the lamination of this product. The inner and outer faces of the windshield are formed of a first glass ply 21 adjacent one face and a second glass ply 22 adjacent the other face. In a typical embodiment these glass plys are about zinch thick. A transparent plastic interlayer 23 is bonded to the first glass ply 21. This interlayer is typically polyvinyl butyral about 0.015 inch thick. A similar transparent interlayer 24 is bonded to the other glass ply 22. The electrically conductive portion of the heatable windshield is bonded between the two interlayers.

which is in the same range as conventional tinted glass.

In the edge portion illustrated in FIG. Zone of the bus bars 11 can be seen overlying the thin metal film 27. Such a bus bar is typically athin copper foil which during the course of laminating imbeds slightlyin the polyvinyl butyral interlayer 23. If desired a conductive adhesive may be employed between the bus-bar 11 and the conductive film 27 to assure uniform continuous electrical contact. A suitable bus bar arrangement is disclosed in U.S. Pat. No. 3,612,745. It should be recognized that the cross section illustrated in FIG. 2 is not drawn to scale and that the metal layer 27 is almost vanishingly thin if seen in cross section. I

It will be noted from FIG. 2 that the two glass plys 21- and 22, the two interlayers 23 and 24 and the carrier film 26 are coextensive and each extends clear to the edge of the windshield. It will be specifically noted that the electrically conductive metal layer 27 terminates some distance from the edge of the windshield. This distance may, for eample, be /(1 to 1% inch, or even greater, being limited only by the requirement that the electrically conductive coating be in electrical contact with the bus bar over a substantial portion of the bus bar area. The conductive layer may be removed throughout the area between the isolation lines l8.and the edge of the window.

In a preferred process for making electrically heatable Windshields, the carrier film is made in large sheets which may, for example, be long rolls of plastic film which are continuously metalized in a vacuum chamber 7 so that substantially'th e entire area of one side of the film is coated with an electrically conductive coating. Thereafter the carrier film is cut to a size and shape corresponding to thesize and shape of the glass plys between which it isto be laminated. In this state the conductive metal film is coterminous with the carrier film. As pointed out hereinabove it has been found that it is undesirable to have the electrically conductive film adjacent the edge of the windshield. Therefore, in practice of this invention the electrically conductive coating is removed from the entire periphery of the carrier film before it is bonded to the interlayer.

A broad variety of techniques have been found suitable f0! removing the conductive layer from the edge portions of the plastic carrier film. Preferably this layer is removed by a technique that abrades the surface of the plastic carrier film thereby giving it some roughness. Suitable techniques include rubbing it with fine sandpaper or similar abrasive, wire brushing, rubbing with a conventional rotating drafting eraser, rubbing with a stiff-bristled rotating brush, sandblasting and the like.'A suitable technique involves rubbing with a stiffbristled brush immediately outside the edges of a central mask that keeps particles off of the conductive coating that remains. Any removed particles can be readily sucked or blown away to keep them off of the masked central conductive area. It will also be recognized that chemical etching can be usedaround the edges, however, this may pose cleaning problems before the window is used. Relatively weak etching reagents are suitable because of the extreme thinness of the metal coatings on the carrier film. An almost universally useful'etching technique involves running a moistened cotton swab over the edge portions where it is desired to remove the metal coating. The swab can, for example, be moistened with a mixture of equal parts of one normal hydrochloric acid and one normal nitric acid. If desired a second swab moistened with distilled water can be used to remove any salts left on the surface. Many other etchants will be apparent for various conductive metal coatings.

The process for making the windshield thus involves forming the glass plys 21 and 22 to the desired size and shape. Cutting the interlayers 23 and 24 to a conforming size and shape and cutting the previously vacuum metallized carrier film to a conforming size and shape. The bus bars are then placed on one face of one of the interlayers and conductive adhesive applied if desired. It is often convenient to lightly tack the bus bars in place on the interlayer adhesively or with gentle heat- After the edge portions of the electrically conductive layer have been removed from the carrier film, either of two courses may be taken. According to one technique one or both of the two interlayers and the plastic ply with the conductive coating thereon are laminated together in what may be known as a prelaminate. This prelaminate subassembly is then fitted between glass plys and the entire assembly laminated at elevated temperature and pressure according to conventional glass laminating techniques. According to the other technique, the two glass plys, two interlayers and carrier film are all assembled in one operation and laminated according to conventional technique without going through the prelaminating step.

The plastic ply and interlayers are at least coextensive with the glass ply and may actually extend a small distance beyond the edges of the glass in the course of manufacturing. Such protruding edges would typically be trimmed off before the windshield is used. On the other hand, if either interlayer or the plastic ply is set back from the edge of the glass by any appreciable amount, there is a high risk of cracking the glass during the laminating process. Thus it has not proved satisfactory to trim the carrier film to an extent smaller than the glass plys for limiting the approach of the conductive coating to the edge of the laminated windshield. Similarly masking of the peripheral portions of the carrier film to inhibit vacuum deposition of the conductive coating is impractical where a continuous deposition process is employed. Mechanical removal of the conductive coating from edge portions of the carrier film has been found to be the only commercially practical technique for making an electrically heatable window at an economical price without electrical hazard at the edges of the window.

Removal of the electrically conductive coating from the peripheral portions of the carrier film by mechanically abrading the surface has been found to have another substantial benefit. Environmental attack apparently by vapor entry in the interface has sometimes caused delamination of portions of windows having a conductive layer extending to the edge. Where the edge of the conductive layer is removed, such delamination virtually never occurs. This is desirable even when high voltage as in a heatable window are not present.

Another benefit lies in the enhanced bond between the interlayer and the carrier film in the region where the conductive coating is removed. The interface where the conductive coating is present is inherently somewhat weaker than a similar interface without the conductive coating. Thus, in a laminated window where the edge portions of the conductive coating has been-removed, a stronger bond is obtained around the periphery of the window. This yields a significantly better product, since spontaneous window delamination and failure initiate in the edge portions. The mechanical action of abrading the surface of the carrier film is an additional benefit since the slight roughness introduced further enhances the bond between the plastic ply and the interlayer.

In the illustrated arrangement the carrier film having a conductive layer thereon is sandwiched between two interlayers which are in turn sandwiched between sheets of glass. Principles of this invention are applicable to other arrangements such as, for example, laminated windows wherein polycarbonate or methyl methacrylate transparent plastics are substituted for the glass plys. In another embodiment a rigid glass ply may be used with a single interlayer and the carrier film on which the conductive metal film is deposited. The carrier film can serve as one face of the window, Many other variations in the detailed design of a window with an electrically conductive layer therein will be apparent to one skilled in the art.

Since many modifications and variations will be apparent it is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. An electrically heatable window comprising seriatim:

a transparent glass ply;

a relatively lower melting transparent plastic interlayer bonded to the glass ply and co-extensive therewith;

at least a pair of electrically conductive bus bars im' bedded in and bonded to the interlayer and being spaced inwardly from the side edges thereof;

an electrically conductive transparent layer having its side edges spaced inwardly from side edges of the glass ply and having edge portions in electrical contact with the bus bars and the balance bonded to the interlayer; and

a relatively higher melting transparent plastic carrier film co-extensive with the glass ply having edge portions bonded to the interlayer and the balance bonded to the electrically conductive layer, and wherein the portion of the transparent carrier film bonded to the electrically conductive layer is relatively smooth and the edge portions bonded to the interlayer are relatively rough.

2. An electrically heatable window as defined in claim 1 further comprising a second transparent plastic interlayer bonded to the face of the carrier film opposite from the electrically conductive layer; and

a second glass ply bonded to the second interlayer, said second interlayer and second glass ply being co-extensive with the first glass ply. 

1. An electrically heatable window comprising seriatim: a transparent glass ply; a relatively lower melting transparent plastic interlayer bonded to the glass ply and co-extensive therewith; at least a pair of electrically conductive bus bars imbedded in and bonded to the interlayer and being spaced inwardly from the side edges thereof; an electrically conductive transparent layer having its side edges spaced inwardly from side edges of the glass ply and having edge portions in electrical contact with the bus bars and the balance bonded to the interlayer; and a relatively higher melting transparent plastic carrier film coextensive with the glass ply having edge portions bonded to the interlayer and the balance bonded to the electrically conductive layer, and wherein the portion of the transparent carrier film bonded to the electrically conductive layer is relatively smooth and the edge portions bonded to the interlayer are relatively rough.
 2. An electrically heatable window as defined in claim 1 further comprising a second transparent plastic interlayer bonded to the face of the carrier film opposite from the electrically conductive layer; and a second glass ply bonded to the second interlayer, said second interlayer and second glass ply being co-extensive with the first glass ply. 